First Complete Electric Power System – 1882
Introduction of AC Systems – 1886
AC vs DC [Tesla vs Edison]
- Voltage levels can be easily transformed in ac systems, thus providing the flexibility for use of different voltages for generation, transmission, and consumption.
- AC generators are much simpler than dc generators.
- AC motors are much simpler and cheaper than dc motors.
The ac versus dc controversy ended with victory for the ac system.
Frequency – 50Hz vs 60Hz
Early AC Systems
- This rose to 165 kV in 1922, 220 1W in 1923, 287 kV in 1935, 330 kV in 1953, and 500 kV in 1965.
- Hydro Quebec energized its first 735 kV in 1966, and 765 kV was introduced in the United States in 1969.
- To avoid the proliferation of an unlimited number of voltages, the industry has standardized voltage levels.
- The standards are 115, 138, 161, and 230 kV for the high voltage (HV) class, and 345, 500 and 765 kV for the extra-high voltage (EHV) class.
HVDC Transmission Systems – 1950s
- The HVDC transmission is attractive for transmission of large blocks of power over long distances. The cross-over point beyond which dc transmission may become a competitive alternative to ac transmission is around 500 km for overhead lines and 50 km for underground or submarine cables.
- HVDC transmission also provides an asynchronous link between systems where ac interconnection would be impractical because of system stability considerations or because nominal frequencies of the systems are different.
- Interconnection of neighbouring utilities usually leads to improved system security and economy of operation. Improved security results from the mutual emergency assistance that the utilities can provide. Improved economy results from the need for less generating reserve capacity on each system.
- In addition, the interconnection permits the utilities to make economy transfers and thus take advantage of the most economical sources of power. These benefits have been recognized from the beginning and interconnections continue to grow.